A flurry of small earthquakes rumbling near the Mammoth Mountain Volcano , have been categorized as `` volcanic unrest '' by the United States Geological Survey .

Nearly three dozen earthquakes ranging from magnitude 2.6 to 3.8 have swarmed the area , northeast of Fresno , California , over the last two days .

Earthquake swarms in this region are not uncommon . David Shelly , a seismologist with California Volcano Observatory , said this swarm is `` bigger than we 've seen recently , but normal in the area . '' He adds they are keeping a close eye on the movement , `` but in the larger scheme of things , it 's within in the range of activity over the last several decades . ''

Mammoth Mountain is in an area called the Long Valley Caldera . The center of the caldera has been uplifting slowly over the last several decades and seismologists continuously monitor it . `` We think there is fluid coming up from the crust triggering the earthquakes , '' said Shelly .

The last swarm of quakes from 1997 to 1998 produced over 2,500 earthquakes per week at its height , according to the USGS . Since then , the region has been relatively quiet .

In July , USGS scientists installed a volcanic-gas monitoring station on the mountain . It tracks gases that fluctuate with earthquake activity to better track the changes in real-time .

The awareness level on the USGS website remains at green/normal . Mammoth Mountain , standing at 11,053 feet , last erupted about 57,000 years ago , according to the USGS .

@highlight

Three dozen earthquakes in last 2 days near Fresno , California

@highlight

Swarms of earthquakes not uncommon in the region

@highlight

Last swarm of earthquakes produced over 2500 between 1997-98